TOXICITY OF 4, 346 CHEMICALS TO LARVAL LAMPREYS 



AND FISHES 



INTRODUCTION 



The problem of controlling the sea lamprey in the upper Great Lakes has received considerable 

 attention in recent years and requires no review here (Applegate and Moffett, 1955). Electromechanical 

 weirs and naps and electrical barriers have been developed which can be successfully employed to block 

 and/or destroy spawning runs of adult sea lampreys. These devices, when installed in all known spawning 

 streams, provide an effective method of reducing the numbers of sea lampreys in each lake basin. Initial 

 efforts at control of the lamprey have employed these devices (Applegate, Smith, and Nielsen, 1952; 

 Erkkila, Smith, and McLain, 1956). 



Unfortunately, however, a sea lamprey control program based on the prevention of spawning 

 will not show results for seven or more years. At least six generations of larvae, spawned previous to the 

 "blockade" of the streams, must grow, transform, migrate to the lakes, and prey on fish before the "blockade" 

 is effective. Such a delay may prove disastrous in Lake Superior where there is evidence that lamprey 

 predation will cause the collapse of the lake trout fishery, as has occurred in Lakes Huron and Michigan, 

 before weir control measures can become effective. 



In view of these facts the principal problem is now one of developing techniques for attacking 

 the sea lamprey which will produce more immediate control of the species. If we could destroy the larvae 

 in the streams we might reduce substantially the parasitic populations in the lakes in less than two years. 

 The introduction of natural enemies has been considered but invariably there is a great risk that "the cure 

 might be worse than the disease". A more direct attack is provided by the use of either indiscriminate or 

 selective poisons. Indiscriminate poisons, which would kill all fish-life in a stream, are undesirable since 

 most streams infected with sea lamprey larvae also contain populations of important game and food fishes. 



The major objective of this investigation was, therefore, to locate chemicals which would be 

 acutely toxic to larval sea lampreys at extremely low concentrations and which, at the same concentrations, 

 would be non-toxic to other fishes inhabiting the same natural environments. 



The initial step in achieving this objective was a preliminary screening of a large and diverse 

 series of predominantly organic chemical substances. Test procedures in this program were designed only 

 to disclose toxicity at low levels in short periods. 



The screening tests revealed some compounds which, at particular concentrations, were more 

 toxic to lamprey larvae than to fishes; others appeared toxic only to the larvae. Among these substances, 

 only two were found to be sufficiently toxic and specific in their action at low concentrations to meet the 

 requirements and objectives of our program. Preliminary data for these two compounds and subsequent 

 studies conducted to determine their usefulness as specific sea lamprey larvicides are not included here; 

 they will be discussed in separate reports. The present report includes all other information obtained in 

 the screening program on the apparent toxic effects of 4, 346 compounds among larval lampreys and two 

 species of fishes. These data are summarized here for the use that may be made of them by industrial 

 chemists, toxicologists, physiologists, fishery scientists, and others. 



